1. Field of the Invention
This invention relates to a method of forming a magneto-optical device and for producing in such device magnetizations of opposite polarities and for producing illuminations in accordance with the polarities of such magnetizations. The invention also relates to a method of producing such a magneto-optical device in which a plurality of pixels are provided for producing an image in accordance with the pattern of illuminations provided in the pixels.
2. Description of Related Art
Devices are known in the prior art for defining a plurality of pixels on a thin magnetizable layer of a thin transparent dielectric substrate. The magnetizable layer is formed from a material capable of being saturated with magnetic fluxes of opposite polarities. When the magnetizable layer is saturated with magnetism of one polarity, the magnetizable material becomes polarized in one direction. The magnetizable layer becomes polarized in an opposite direction when it is saturated with magnetism of an opposite polarity. When light is directed to the magnetizable layer, the light passes through the epitaxial layer when the layer is polarized in one direction. The passage of light through the epitaxial layer is blocked when the magnetizable layer is polarized in the opposite direction. In this way, a visual image can be provided in the device.
The devices described in the previous paragraph have been disclosed and claimed in a number of patents including the following assigned of record to Litton Industries, Inc., of Beverly Hills, Calif. U.S. Pat. Nos.:
4,478,872 PA0 4,497,545 PA0 4,500,176 PA0 4,500,177 PA0 4,563,236 PA0 4,578,321
The devices described above divide the magnetizable layer into a plurality of pixels by providing electrical lines on the magnetizable layer in a matrix relationship. Each pixel may have a length of only a relatively few microns such as in the order of approximately twenty microns (20.mu.) to approximately two hundred and fifty microns (250.mu.) and may have a corresponding or different width. By providing the pixels with such a small area in the matrix arrangement and by saturably magnetizing the pixels on a selective basis with opposite polarities to illuminate the pixels on such a selective basis, a visual image can be produced in the matrix when a polarized light is introduced to the matrix.
The visual displays discussed in the previous paragraphs have certain important advantages. One advantage is that a large number of pixels can be disposed in a small area so that a compact image can be provided for a finite number of pixels. Alternatively, an image of high resolution can be provided by enlarging the image and increasing the number of pixels in the image. However, the visual display described above has certain significant disadvantages. One disadvantage is that the magnetic force required to provide the magnetizable layer with a saturable magnetization in the two opposite polarities is relatively large. Another disadvantage is that the intensity of the light transmitted through the pixels is relatively low because of high absorption coefficients in the pixels.
A further disadvantage results from the fact that the pixels are formed by raised portions and that the conductors for magnetizing the pixels are disposed in troughs between the raised portions. Since the corners of the pixels are sharp, discontinuities are produced in the conductors at the pixel corners. These discontinuities have often prevented the illuminating systems defined by the pixels from operating satisfactorily.
There is another significant disadvantage in the illuminating systems of the prior art. This has resulted from the fact that an isolated position, or isolated positions, in each pixel have had to be doped. The doping has had to be provided to facilitate the magnetization of the individual pixels by the passage of current through the conductors associated with such individual pixels.
In the illuminating systems of the prior art, a coil has had to envelope the pixel matrix. After the individual pixels have been magnetized, a current has been passed through the coil to saturate the magnetization of the pixels previously magnetized in one polarity. This insures that the polarized light will pass through these pixels. After the image in the pixel matrix has been illuminated, a current has had to be passed in one direction through the coil to produce the same magnetization in all of the pixels. This has prepared the pixel matrix to display another visual image.
The use of the enveloping coil is disadvantageous for several reasons. The coil requires the use of an additional component in the illuminating system. It increases the area occupied by the pixel matrix. The coil requires relatively large amounts of power since it operates on all of the pixels, particularly when the pixels are being magnetized in a unitary direction after an image has been produced. It also slows significantly the operation of the system in providing successive images.
The disadvantages discussed in the previous paragraphs have existed for some time. In spite of considerable efforts to overcome these disadvantages, the disadvantages have continued to exist. The illuminating systems now in use are slow, cumbersome and require considerable amounts of power to produce images which are of limited sharpness and clarity.